1. Field of Invention
The invention relates to a method of operating an internal combustion engine of a vehicle, and more particularly, to the method of operating an internal combustion engine having an electromagnetically driven intake valve.
2. Description of Related Art
Conventionally intake valves or exhaust valves of an internal combustion engine have been operated by a cam of a cam shaft that is driven by a crank shaft synchronously. Recent advancement in a control technology using a computer has allowed operation of the intake or exhaust valves by an electromagnetic actuator. The resultant expanded range of the valve operation timing makes it possible to control operation of the internal combustion engine especially for a vehicle in various modes. The aforementioned technology for controlling the operation is disclosed in JP-A-2000-73800, 2001-182570, and 2001-193504, for example.
FIG. 1 is a schematic cross sectional view of the electromagnetically driven intake valve that corresponds to the view shown in FIG. 2 of JP-A 2001-193504. Referring to FIG. 1, an intake port 26 has an open end around which a valve seat 200 is provided. The open end is opened and closed by a valve 28a of the intake valve. The valve 28a is connected to a valve shaft 28b that is vertically guided by bushing 201 so as to move up and down. The valve 28a is designed to move between a valve opening position and a valve closing position by an electromagnetic drive system 30.
The electromagnetic drive system 30 includes a housing 300, a valve closing core 301, a valve opening core 302, a valve closing coil 303, a valve opening coil 304, and an armature 305 that is carried by the valve shaft 28b and moves between a valve closing electromagnetic device having the valve closing core 301 and the valve closing coil 303 and a valve opening electromagnetic device having the valve opening core 302 and the valve opening coil 304. The electromagnetic drive system 30 further includes compression coil springs 306, 307 that serve to elastically bring the armature 305 into a center position between the electromagnetic devices when no electric current is applied to the coils 303 nor 304.
Referring to FIG. 1, an intake valve lift sensor 40 is directly assembled onto the electromagnetic drive system 30. The lift sensor 40 includes a housing 400 connected to the housing 300 of the electromagnetic drive system 30, a disc-like target 401 attached to the upper end of the valve shaft 28b within the housing 400, and a gap sensor 402 that is provided in the housing 400 so as to detect displacement of the target 401.
During operation of the internal combustion engine having the aforementioned electromagnetically driven intake valve, an appropriate electric controller switches supply of electricity between the valve closing coil and the valve opening coil in accordance with a rotating phase of the crank shaft of the engine. As a result, the intake port is closed by switching the supply of electricity to the intake valve closing coil 303. The intake port is opened by switching the supply of electricity to the intake valve opening coil 304.
In the electromagnetic drive system including the cores, coils, armature and springs, a positional deviation of the armature is not caused by the positional restriction, that is, contour of the cam in operation but caused by imbalance of the force. Accordingly opening and closing of the valve operated in response to the electric command signals that command opening and closing of the valve may deviate from a predetermined normal characteristic at every opening and closing valve operation in response to the electric command signals. The valve is tightly seated on the valve seat in the closed state in which friction force that is likely to disperse acts between the valve and the valve seat. Especially in the case where an annular shoulder portion of the intake valve or the exhaust valve of the internal combustion engine abuts on the annular valve seat along the respective center axes, the frictional force acting between the valve and the valve seat may vary depending on concentricity of those elements. The friction drag acting on the valve at a time when the valve is opened from the closed state may vary among a plurality of valves each being identically designed. Furthermore, the friction drag acting on the single valve may also vary at every opening and closing operation. As the timing for opening the intake valve is partially overlapped with the timing for closing the exhaust valve, a small difference in the valve opening characteristic may influence the operation performance of the engine after the air intake state has been changed. Even if the intake valve opening timing is slightly deviated from the control target value, the desired effect cannot be obtained in the control for operating the engine.
The deviation of the valve opening operation from the normal characteristic may also occur in the exhaust valve owing to dispersion in the friction of engagement between the valve and the valve seat. As the opening operation of the exhaust valve is not overlapped with the opening operation nor closing operation of the intake valve, the slight dispersion in the opening characteristics of the exhaust valve may be negligible in view of controlling the operation of the internal combustion engine.